[PATCH v5 4/6] ksm: count zero pages for each process

[PATCH v5 4/6] ksm: count zero pages for each process

[yang.yang29]

From: xu xin <xu.xin16@zte.com.cn>

As the number of ksm zero pages is not included in ksm_merging_pages per
process when enabling use_zero_pages, it's unclear of how many actual
pages are merged by KSM. To let users accurately estimate their memory
demands when unsharing KSM zero-pages, it's necessary to show KSM zero-
pages per process.

since unsharing zero pages placed by KSM accurately is achieved, then
tracking empty pages merging and unmerging is not a difficult thing any
longer.

Since we already have /proc/<pid>/ksm_stat, just add the information of
zero_pages_sharing in it.

Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
Cc: Xiaokai Ran <ran.xiaokai@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: xu xin <xu.xin16@zte.com.cn>
---
 fs/proc/base.c           | 1 +
 include/linux/mm_types.h | 7 ++++++-
 mm/ksm.c                 | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9e479d7d202b..ac9ebe972be0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3207,6 +3207,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
 	mm = get_task_mm(task);
 	if (mm) {
 		seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
+		seq_printf(m, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
 		mmput(mm);
 	}

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4e1031626403..5c734ebc1890 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -776,7 +776,7 @@ struct mm_struct {
 #ifdef CONFIG_KSM
 		/*
 		 * Represent how many pages of this process are involved in KSM
-		 * merging.
+		 * merging (not including ksm_zero_pages_sharing).
 		 */
 		unsigned long ksm_merging_pages;
 		/*
@@ -784,6 +784,11 @@ struct mm_struct {
 		 * including merged and not merged.
 		 */
 		unsigned long ksm_rmap_items;
+		/*
+		 * Represent how many empty pages are merged with kernel zero
+		 * pages when enabling KSM use_zero_pages.
+		 */
+		unsigned long ksm_zero_pages_sharing;
 #endif
 #ifdef CONFIG_LRU_GEN
 		struct {
diff --git a/mm/ksm.c b/mm/ksm.c
index 72c0722be280..083f5d125373 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -794,6 +794,7 @@ static inline void clean_rmap_item_zero_flag(struct ksm_rmap_item *rmap_item)
 {
 	if (rmap_item->address & ZERO_PAGE_FLAG) {
 		ksm_zero_pages_sharing--;
+		rmap_item->mm->ksm_zero_pages_sharing--;
 		rmap_item->address &= PAGE_MASK;
 	}
 }
@@ -2117,6 +2118,7 @@ static int try_to_merge_with_kernel_zero_page(struct ksm_rmap_item *rmap_item,
 			if (!err) {
 				rmap_item->address |= ZERO_PAGE_FLAG;
 				ksm_zero_pages_sharing++;
+				rmap_item->mm->ksm_zero_pages_sharing++;
 			}
 		} else {
 			/* If the vma is out of date, we do not need to continue. */
-- 
2.15.2

Re: [PATCH v5 4/6] ksm: count zero pages for each process

[David Hildenbrand]

On 30.12.22 02:16, yang.yang29@zte.com.cn wrote:
> From: xu xin <xu.xin16@zte.com.cn>
> 
> As the number of ksm zero pages is not included in ksm_merging_pages per
> process when enabling use_zero_pages, it's unclear of how many actual
> pages are merged by KSM. To let users accurately estimate their memory
> demands when unsharing KSM zero-pages, it's necessary to show KSM zero-
> pages per process.
> 
> since unsharing zero pages placed by KSM accurately is achieved, then
> tracking empty pages merging and unmerging is not a difficult thing any
> longer.
> 
> Since we already have /proc/<pid>/ksm_stat, just add the information of
> zero_pages_sharing in it.
> 
> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
> Cc: Xiaokai Ran <ran.xiaokai@zte.com.cn>
> Cc: Yang Yang <yang.yang29@zte.com.cn>
> Signed-off-by: xu xin <xu.xin16@zte.com.cn>
> ---
>   fs/proc/base.c           | 1 +
>   include/linux/mm_types.h | 7 ++++++-
>   mm/ksm.c                 | 2 ++
>   3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 9e479d7d202b..ac9ebe972be0 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3207,6 +3207,7 @@ static int proc_pid_ksm_stat(struct seq_file *m, struct pid_namespace *ns,
>   	mm = get_task_mm(task);
>   	if (mm) {
>   		seq_printf(m, "ksm_rmap_items %lu\n", mm->ksm_rmap_items);
> +		seq_printf(m, "zero_pages_sharing %lu\n", mm->ksm_zero_pages_sharing);
>   		mmput(mm);
>   	}
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 4e1031626403..5c734ebc1890 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -776,7 +776,7 @@ struct mm_struct {
>   #ifdef CONFIG_KSM
>   		/*
>   		 * Represent how many pages of this process are involved in KSM
> -		 * merging.
> +		 * merging (not including ksm_zero_pages_sharing).
>   		 */
>   		unsigned long ksm_merging_pages;
>   		/*
> @@ -784,6 +784,11 @@ struct mm_struct {
>   		 * including merged and not merged.
>   		 */
>   		unsigned long ksm_rmap_items;
> +		/*
> +		 * Represent how many empty pages are merged with kernel zero
> +		 * pages when enabling KSM use_zero_pages.
> +		 */
> +		unsigned long ksm_zero_pages_sharing;

Same comment as for previous patch: this counts rmap itmaps, no? 
ksm_zero_rmap_items might be more appropriate.

-- 
Thanks,

David / dhildenb